A CD-ROM Appendix is submitted herewith and is incorporated herein by reference in accordance with 37 CFR xc2xa7 1.52. The Appendix comprises a single CD-ROM, created on Jul. 19, 2001 that includes one file, entitled xe2x80x9cCD ROM Appendix.PDFxe2x80x9d. This file includes the control system equations and their derivation for one exemplary embodiment of the invention. The appendix is in PDF format and may be viewed using the Adobe(copyright) Acrobat(copyright) Reader.
1. Field of the Invention
The present invention relates to control systems and, more specifically, to a tracking control design applied to an electronic throttle system.
2. Description of the Prior Art
An electronic throttle control system controls the opening of a throttle valve by driving a direct current (DC) motor in accordance with a desired throttle position requested from high level control. In this throttle control, pulse width modulated duty cycle ratio is generated based on throttle position measurement and a desired position signal from a higher level control or an accelerator position sensor which detects the accelerator position corresponding to the depression amount of the accelerator pedal. The PWM with a properly calculated duty cycle ratio will drive the DC motor through the gear train to open or close the throttle valve to the exact desired position to control an intake air amount to the engine. A feedback control of the proportional, integral and derivative (PID) control is performed on the DC motor to reduce errors between a signal from a throttle opening sensor which detects an actual throttle opening of the throttle valve and the desired position signal which can be signal measured from an accelerator position sensor (in pedal follower mode) or a signal generated from a higher level control.
It has been a general design practice to determine each control constant of P(proportional)-term, I(integral)-term and D(derivative)-term of the PID control to fixed intermediate values to meet requirements under all operating conditions of the system. Since the control constants thus determined do not become the optimum values for specific operating conditions, particularly in non-linear systems, responsiveness and stability of the throttle valve control may be degraded. For example, during an idle speed control which stabilizes an engine rotational speed to a predetermined speed under engine idle conditions, the response speed of the throttle valve may be low but the stability must be high and the control should be robust to any disturbances, such as battery voltage drop. Furthermore, during a traction control that optimally controls the force of driving wheels driven by the internal combustion engine in accordance with road surface conditions, the stability of the throttle valve may be lowered to some extent but the response speed must be maintained high. When using cruise control, which controls a constant speed running of a vehicle without operating an accelerator pedal, both high responsiveness and stability are required. The goal of the control is to achieve fast and stable tracking in all circumstances.
The fixed intermediate values of the constants used in existing PID controllers are not optimal for each range of use. Some existing controllers compensate for this by applying gain scheduling PID control, i.e., a different set of constants for each range of use. However, the added complexity associated with doing so reduces dynamic tracking performance and degrades the robustness of the system. Furthermore, calibration of all control parameters at different operating conditions requires extensive work.
Therefore, there is a need for a robust electronic throttle control system that is responsive, robust and fast tracking.